Thermophysical modeling of Didymos’ moon for the Asteroid Impact Mission

Significance Statement

The study of binary systems is essential for space missions like the proposed Asteroid Impact Mission, which target primary and secondary asteroidal bodies. Didymos is a binary system that consists of a larger primary and a smaller secondary. The attributes of the main body in the Didymos system are characterized through radar observations and photometric methods. It has been found that, of all secondary orbital periods identified as of the moment, that of Didymos is the shortest with an approximate value 11.9h. While the main body’s rotational period is determined as 2.6h, the secondary rotational period could not be derived easily. A synchronous rotation however is compatible with observations, in the sense that the rotational period is equal to the secondary orbital period. Modeling daily temperature variations of Didydmos’ moon in the course of the mission is of great importance when it comes to investigating the thermal survivability of the MASCOT-2 lander and designing the thermal imager, two of the payloads of the Asteroid Impact Mission.

Thermal emission of the secondary in the binary system is dependent on the shape, spin vector, thermal inertia, solar distance, surface roughness and size of the secondary as well as shadowing and thermal radiation from the primary. All these parameters can be incorporated in the thermophysical model to estimate the thermal emission of the moon. Ivanka Pelivan and colleagues at the DLR Institute of Planetary Research and DLR-MUSC, Space Operations and Astronaut Training in Germany performed the thermosphysical modeling of the Didymos’ secondary based on the current understanding of the physical characteristics of the moon. Owing to the unknown thermal inertia, they covered a broad range of thermal inertia in their simulation. Their work is published in Advances in Space Research.

The authors modelled the Didymos’ secondary through a simplified approach owing to the several assumptions and unknowns that had to be adopted. Neglected effects however were shown to be small at least when compared to the uncertainty in thermal inertia. While the full thermophysical model included direct and diffuse solar radiation and direct as well as diffuse self-heating, in this study the diffuse terms as well as direct self-heating do not play a role due to the ellipsoidal model shape assumption.

The research team was able to establish a thermophysical model of the secondary in the Didymos system. They selected a case study that entailed a wide range of thermal inertia with and without shadowing effects of the primary. Their computations were based on analytical formulations of an ellipsoid, but the model could also accommodate complex shape models with quadrilateral and triangular facets allowing an in-depth investigation of thermal conditions of realistic shapes.

Using the thermophysical model results for a thermal infrared imager performance study, it was found that the proposed thermal imager covers the range of peak emission for the likely range of thermal inertia. Furthermore, applying the thermophysical model with high as well as low thermal inertia, the authors were able to evaluate the performance of the MASCOT-2 lander for a number of possible landing sites as well as specific settings. For all cases considered, they found that the temperatures were mostly within operating limits except for one case of latitude +45 degrees, which was, fortunately, outside the desired landing range.

About The Author

Ivanka Pelivan received her PhD degree in 2013 at the University of Bremen with a thesis about a specialized satellite dynamics and environment simulator for a scientific class of Earth-bound satellites. As a Marie-Curie fellow at Stanford University she applied the developed software library to the relativity mission Gravity Probe B for data post-processing. She currently holds a HGF-Postdoc position that aims at further development of the satellite software library for solar system missions with focus on missions like Rosetta, Hayabusa-2 and AIM.

In 2012 she joined the DLR Institute of Planetary Research and has been actively involved in preparation of data analysis for the Rosetta instrument MUPUS in performing environment thermal modelling. As ROLIS (down-facing camera on Rosetta’s lander Philae) operations engineer she was responsible for test and generation of the camera command sequences and camera operation in flight. Currently she also coordinates a work package in the EU Horizon2020 project MiARD.

About The Author

Line Drube is a planetary scientist educated from 1) the Niels Bohr Institute at University of Copenhagen, 2) the Earth, Planetary, and Space Science Department at University of California Los Angeles (UCLA), and 3) the International Space University. Since 2012 she has worked in the Institute for Planetary Research at the German Aerospace Center in Berlin on first European Commission’s NEOShield project “A Global Approach to Near-Earth Object Impact Threat Mitigation” and later on the NEOShield-2 project “Science and Technology for Near-Earth Object Impact Prevention“.

Her work includes investigation into the physical properties of asteroids and research relevant for space missions to deflect asteroids. In the United Nation Space Missions Planning Advisory Group (SMPAG) for the Committee for the Peaceful Uses of Outer Space she has as part of the German delegation worked on the team’s recommendations to the UN for a coordinated international response to the NEO impact threat, as well as being the coordinator of the SMPAG’s Ad-hoc Working Group on Legal Issues.

About The Author

Ekkehard Kührt obtained his PhD degree in 1982 in solid-state physics at the Humboldt University Berlin. Since then he has been working in planetary physics and has focused on minor bodies. He has been the head of the “Asteroids&Comets” Department at the Institute of Planetary Research of German Aerospace Center (DLR) since 1997. During sabbaticals he stayed at the Max-Planck-Institute (MPS) in Katlenburg-Lindau (1991 and 1994), at the South West Research Institute San Antonio/TX (1994) and the International Space Science Institute in Bern (2009, 2016). He was granted the Humboldt-Award of the Humboldt-University (1982), the Award for Young Scientists of the Leopoldina-Academy (1993), the Otto-Lilienthal-Award of DLR (2009), the Space Technology – Hall of Fame Award of US Space Foundation (2012) and the Europlanet Prize for Public Outreach (2017).

With his involvements in space missions (e.g. Russian VEGA-Halley and Phobos missions, JAXA/Hayabusa-2 mission, ESA/ROSETTA experiments MUPUS, OSIRIS, RPC, and VIRTIS) he could gather experiences in analyzing data of space experiments. He is author and co-author of more than 150 scientific publications. Presently, he is responsible for the DLR project “Rosetta instruments” and coordinates the DLR involvements in the EU Horizon2020 project MiARD.

About The Author

Jörn Helberts background is in Physics (graduation in 1998). Since 2003 he is working as a staff scientist at the German Aerospace Center, currently leading the “Planetary spectroscopy laboratory group”.

His main expertise is in planetary remote sensing using infrared techniques. To that purpose he created the Planetary Emissivity Laboratory (PEL) of DLR, which is now one of the leading laboratories for the study of planetary analogue materials. Its capabilities to measure samples at temperatures up to 1000°C makes it worldwide unique.

Jörn Helbert gained a lot of experience in project management as CoPI of the MERTIS instrument on BepiColombo. To formalize this he attended a 2 years program at the Helmholtz academy for leadership and received a degree as certified manager.

Apart from BepiColombo he is involved in several other space missions including MarsExpress, VenusExpress, the NASA MESSENGER mission to Mercury and the JAXA Hayabusa 2 sample return mission.

Public outreach is an important part of his work and he has a long standing experience as a member of the institutes outreach team in giving public lectures, school class programs and hands on activities. In addition he taught several classes on remote sensing at the Humboldt University in Berlin.

About The Author

Jens Biele works as a senior staff scientist at DLR (German Aerospace Center) in Cologne, Germany. He is involved in the Rosetta Lander and Hayabusa-2 Mascot lander projects as payload manager and scientist and has also been involved in a number of solar system exploration studies. Before his current position, he spent one year as a Postdoc with the Max-Planck-Institute for Chemistry in Mainz. He obtained his PhD in 1998 in geosciences at the Free University Berlin while doing atmospheric research with the Alfred-Wegener-Institute for Polar and Marine Research.

He studied experimental physics at the University of Kaiserslautern and at Imperial College, London.

His field of special expertise is cometary science, regolith mechanical properties as well as probes, payloads and small systems, in particular landers, for missions to small bodies in the solar system.

About The Author

Michael Maibaum is a Spacecraft Engineer at the Microgravity User Support Center of DLR. He became a Diplom-Ingenieur at the Technical University of Aachen RWTH in 1995, where the studies focused on space propulsion systems, spacecraft system engineering and small satellites. He worked throughout the project lifetime for the lander Philae as part of the ESA comet mission Rosetta starting with the design and implementation of the Thermal Control System and continuing as System Engineer and Operations Engineer until end of mission.

Currently he is leading the Thermal Control System and working as Operations Engineer on the lander Mascot as part of the JAXA asteroid project Hayabusa-2.

Parallel to the active projects he is supporting the design, analysis and implementation of Thermal Control Systems for various studies and projects like the framing cameras for the DAWN mission, Material Science Laboratory MSL on ISS or Mascot-2 as part of the AIM mission to the asteroid Didymos.

About The Author

Barbara Cozzoni completed a Master of Science in Nuclear Physics at the University “Alma Mater Studiorum” of Bologna, Italy, with top grades in 1998.

After a fellowship of one year at the European Centre for Nuclear Research – CERN (Geneva, Switzerland) in 1999, she moved to the space business working at the European Space Agency from 2000 to 2006. At ESA Barbara worked in the mission ENVISAT, the world’s largest civilian Earth observation satellite, and gained experiences in ground segment operations and procedures, in satellite instrumentations and in data processing and calibration.

In 2006 she moved to the European Organisation for the Exploitation of Meteorological Satellites – EUMETSAT (Darmstadt, Germany), where she provided consultancy support during operations in the frame of the MeteoSat Transition Program, MTP, and of the MeteoSat Second Generation Program, MSG, in particular with regards to the image processing facilities, defining, integrating, testing and validating numerical algorithms for data processing.

Since 2011, Barbara is employed at the German Aerospace Center DLR (Cologne, Germany) as operation and thermal engineer participating in the Philae project, the lander of the European mission ROSETTA, until 2015 and currently is involved in the MASCOT project, the lander of the HAYABUSA mission. She supports the planning, the preparation and the validation of nominal and contingency in-flight operations during all mission phases as well as the spacecraft in-flight operations monitoring, telemetry analysis, failure investigation and recovery procedures preparation. She is also responsible of the development of the spacecraft’s thermal mathematical models, used to support the planning of in-flight operations especially during the landing phase.

About The Author

Valentina Lommatsch received her Bachelor in 2010 at the Ohio State University in Mechanical Engineering, followed up in 2013 with a Master of Science in Aerospace Engineering at the FH Aachen University of Applied Sciences, Germany. Since April 2013 she has been part of the Philae Operations Team at the Lander Control Center of the Microgravity User Support Center of DLR focusing on the analysis and prediction of the performance of the lander solar array system and supporting the thermal control team. Following Philae she was working as Operations Engineer for the Material Science Laboratory MSL on ISS and as Operations Engineer on the lander Mascot as part of the JAXA asteroid project Hayabusa-2 and supporting the design of Mascot-2 as part of the AIM mission to the asteroid Didymos.